A media handling subsystem transports a media sheet through a printing apparatus, such as a computer printer, fax machine or copy machine, for imaging. A media sheet is picked from a stack, typically in a tray, then moved along a media path using drive rollers. Along the media path, the media sheet is positioned relative to an imaging mechanism, such as an ink or toner cartridge or printhead, which forms character and/or graphic markings on the media sheet.
For drum based printers, for example, a sheet is fed to the rotating drum by a sheet feeder, and a vacuum captures it and rolls it on to the drum. In scanning-carriage printing systems, such as inkjet printers for example, printheads are typically mounted on a carriage that is moved back and forth across the print media. As the printheads are moved across the print media, the printheads are activated to deposit or eject ink droplets onto the print media to form text and images. The print media is generally held substantially stationary while the printheads complete a “print swath”, typically an inch or less in height; the print media is then advanced between print swaths. The need to complete numerous carriage passes back and forth across a page has meant that such printers have typically been significantly slower than some other forms of printers, such as laser printers, which can essentially produce a page-wide image.
The ink ejection mechanisms of inkjet printheads are typically manufactured in a manner similar to the manufacture of semiconductor integrated circuits. The print swath for a printhead is thus typically limited by the difficulty in producing very large semiconductor chips or “die”. Consequently, to produce printheads with wider print swaths, other approaches are used, such as configuring multiple printhead dies in a printhead module, such as a “page wide array”. Print swaths spanning an entire page width, or a substantial portion of a page width, can allow inkjet printers to better compete with laser printers in print speed.
One type of printing system utilizes multiple printhead modules that each print a substantial portion of a page width; the modules are on carriages that need to be accurately positioned such that visible print defects are not introduced where the separately-printed portions of the page meet.
In order to ensure accurate media or image registration of the printing system, the print engine needs to correlate reference coordinates in both the drum spin or media advance direction (e.g. X-direction) as well as in the carriage motion direction (e.g. Y-direction). Such reference coordination is needed to register the media according to required print margins (e.g. 2 millimeter (mm) print margin). Furthermore, the print engine needs to know where the media is loaded onto the drum relative to the carriages so as to know where to move the carriages and when to trigger the start of printing.